In January 1998 the town of Katherine, approximately 280 km south of Darwin, was extensively flooded. In the aftermath of the flood, the Medical Entomology Branch (MEB) of the Centre for Disease Control (CDC) in the Department of Health and Community Services (DHCS) carried out large-scale mosquito control operations, which reduced mosquito numbers and prevented an outbreak of mosquito borne disease.On 7 April 2006 Katherine was again flooded. Katherine has a seasonal risk of the mosquito borne disease, including Murray Valley encephalitis (MVE), which has a peak risk from March to June in the Top End. Mosquito monitoring in Katherine just before the flood showed relatively high numbers of Culex annulirostris, the main mosquito vector of MVE, which indicated that mosquito control was required urgently to prevent a possible outbreak of disease, as well as to prevent a major pest problem from mosquitoes.